To improve the toughness of propylene polymers and in particular to improve the toughness in the temperature range below 0° C., it is customary to add polymers which are noncrystalline or have a low crystallinity, e.g. ethylene-propylene copolymers, as impact modifiers to propylene polymers. It has been found to be most economical if the impact-modified propylene polymers are prepared directly in a multistage polymerization process. Such products are referred to as high-impact propylene copolymers, as multiphase propylene copolymers, as heterophase propylene copolymers or as propylene block copolymers. The less soft propylene polymer, which normally makes up the largest proportion by weight of the polymer composition, usually forms a physically coherent phase which is referred to as the matrix.
EP-A 918 068 discloses blends of polypropylene and finely divided polyethylene for the production of stiff and transparent films. The polyethylene content does not exceed 10% by weight.
U.S. Pat. No. 5,280,074 relates to a polypropylene molding composition comprising:                (1) 20 to 99% by weight of a crystalline polymer containing at least 95% by weigh of propylene and        (2) 1 to 80% by weight of a non crystalline ethylene-propylene copolymer having an ethylene content of 20% to 90% by weight.        
WO 2004/011507 relates to propylene polymer composition comprising a propylene homopolymer or a propylene copolymer comprising at least 85% of propylene and an ethylene copolymer containing at least 90% by weight of ethylene. The ethylene copolymer ranges from 10 to 50% by weight in the composition and the propylene polymer composition has a melt flow rate of from 2 to 50 g/10 min.